共查询到20条相似文献,搜索用时 0 毫秒
1.
S. Elhamri W. C. Mitchel W. D. Mitchell R. Berney G. R. Landis 《Journal of Electronic Materials》2006,35(4):599-604
Magnetoresistance measurements were performed on van der Pauw shaped AlGaN/GaN heterostructures grown on either sapphire or
silicon carbide. These measurements revealed the presence of Shubnikov-de Haas oscillations. However, the amplitude of the
oscillations originating from perpendicular van der Pauw positions were not isotropic. This anisotropy varied from sample
to sample and within a sample its magnitude changed with the carrier density which was modulated by illumination as it induced
a persistent photocurrent. The results of this study suggest the anisotropy is either a manifestation of electron density
inhomogeneities and/or an indication of a nonuniform scattering mechanism arising from nonuniform interface roughness. 相似文献
2.
D. W. Gotthold S. P. Guo R. Birkhahn B. Albert D. Florescu B. Peres 《Journal of Electronic Materials》2004,33(5):408-411
The AlGaN/GaN heterostructure field-effect transistors (HFETs) were grown on 4H-SiC substrates by metal-organic chemical-vapor
deposition (MOCVD) with a range of Al compositions (30–35%) and AlGaN barrier thicknesses. Films with higher strains exhibited
a time-dependent degradation of the two-dimensional electron gas (2DEG) that varied from days to weeks. Atomic force microscopy
(AFM) measurements of the degraded films revealed a hexagonal cracking pattern with an increase in the medium-scale surface
roughness. The localized strain relaxation of AlGaN barriers and increased roughness of the AlGaN/GaN interface and AlGaN
surface result in a broad shoulder at the lower angle of the AlGaN peak and a loss of satellite fringes in the (0006) reflection
x-ray diffraction (XRD) curve. This degradation raises serious questions with regard to reliability and survivability of AlGaN
HFETs and may complicate device fabrication. 相似文献
3.
M. Ahoujja W. C. Mitchel S. Elhamri R. S. Newrock D. B. Mast J. M. Redwing M. A. Tischler J. S. Flynn 《Journal of Electronic Materials》1998,27(4):210-214
We have experimentally determined the effective mass (m*) of GaN, the classical (τ
c), and quantum (τ
q) scattering times for a two-dimensional electron gas residing at the interface of an AlGaN/GaN heterostructure, using the
Shubnikovde Haas effect. The ratio of the two scattering times, τ
c/τ
q, suggests that, at low temperatures, the scattering mechanism limiting the mobility is due to remote ionized impurities located
in AlGaN. This study should provide sample growers with information useful for improving the quality of the nitride heterostuctures. 相似文献
4.
The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported. Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure. The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region. The buffer trap is suggested to be related to the wide region of high transconductance. The RF characteristics are also studied. 相似文献
5.
正The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported.Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure.The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region.The buffer trap is suggested to be related to the wide region of high transconductance.The RF characteristics are also studied. 相似文献
6.
A novel wet etching method for AlGaN/GaN heterojunction structures is proposed using thermal oxidation f ollowed by wet etching in KOH solution.It is found that an AlGaN/GaN heterostructure after high temperature oxidation above 700℃could be etched off in a homothermal(70℃) KOH solution while the KOH solution had no etching effects on the region of the AlGaN/GaN heterostructure protected by a SiO2 layer during the oxidation process.A groove structure with 150 nm step depth on an AlGaN/GaN heterostructure was formed after 8 h thermal oxidation at 900℃followed by 30 min treatment in 70℃KOH solution.As the oxidation time increases,the etching depth approaches saturation and the roughness of the etched surface becomes much better.The physical mechanism of this phenomenon is also discussed. 相似文献
7.
Y. Q. Tao D. J. Chen Y. C. Kong B. Shen Z. L. Xie P. Han R. Zhang Y. D. Zheng 《Journal of Electronic Materials》2006,35(4):722-725
Transport properties of the two-dimensional electron gas (2DEG) in fully strained and partially strain-relaxed Al0.22Ga0.78N/GaN heterostructures at temperatures from 300 to 680 K have been investigated by Hall effect measurements. The 2DEG mobility
was found to decrease rapidly with increasing temperature at the initial stage and then decrease slowly as temperature is
further increased. Those features indicate strongly that the 2DEG mobility is primarily limited by LO phonon scattering processes
at high temperatures. Meanwhile, the calculated results show that more electrons transfer to the higher-order sub-bands with
increasing temperature, and hence the effect of screening on LO phonon scattering is weakened and the alloy scattering of
the AlGaN layer on the 2DEG becomes stronger. Thus variation of 2DEG occupation in different sub-bands with increasing temperature
also decreases mobility of the 2DEG. 相似文献
8.
用Silvaco的ATLAS软件模拟了栅场板参数对AlGaN/GaN HEMT中电场分布的影响.模拟结果表明,场板的加入改变了器件中电势的分布情况,降低了栅边缘处的电场峰值,改善了器件的击穿特性;场板长度(LFP,length of field plate)、场板与势垒层间的介质层厚度t等对电场的分布影响很大.随着LFP的增大、t的减小,栅边缘处的电场峰值Epeak1明显下降,对提高器件的耐压非常有利.通过对相同器件结构处于不同漏压下的情况进行模拟,发现当器件处于高压下时,场板的分压作用更加明显,说明场板结构更适合于制备用作电力开关器件的高击穿电压AlGaN/GaN HEMT. 相似文献
9.
10.
为了研究适合Ka波段AlGaN/GaN HEMT的栅结构尺寸,借助二维器件仿真软件Silvaco Atlas,在完善仿真模型的基础上研究了Γ型栅各部分对AlGaN/GaN HEMT特性的影响,包括栅长与短沟道效应的关系、栅与沟道距离对短沟道效应和饱和漏电流的影响,以及栅金属厚度对fmax,栅场板对fT、fmax和内部电场的影响。根据典型器件结构和材料参数的仿真表明,为了提高频率并减轻短沟道效应,栅长应取0.15~0.25μm;减小栅与沟道的距离可略微改善短沟道效应,但会明显降低器件的饱和漏电流,综合考虑栅调制能力、饱和漏电流、短沟道效应三个方面,栅与沟道距离应取10~20nm;为了提高fmax,栅金属厚度应大于0.4μm;缩小栅场板长度可有效提高器件的频率,兼顾Ka波段应用和提高击穿电压,栅场板长度应在0.3~0.4μm左右。仿真得出的器件性能随结构参数的变化趋势以及尺寸数据对于Ka波段AlGaN/GaN HEMT的研究具有参考意义。 相似文献
11.
基于静电学分析,得出表面态是电子的一个重要来源.基于这一分析,可以解释已发表的关于二维电子气(2DEC)的大量数据.例如,2DEG密度随着AlGaN层厚度、Al组分的变化的原因.当A10.3Ga0.7N/GaN结构中生长一层5 nm厚的GaN冒层时,2DEG浓度由1.47×1013cm-2减少到1.20×1013cm-2,减少是由于表面类施主态离化减少.由于充分厚的GaN冒层导致GaN/AlGaN/GaN上界面形成二维空穴气(2DHG),所以在超出特定的冒层厚度时2DEG浓度达到饱和. 相似文献
12.
K. V. Smith E. T. Yu J. M. Redwing K. S. Boutros 《Journal of Electronic Materials》2000,29(3):274-280
Local electronic properties in AlxGa1−xN/GaN heterostructure field-effect transistor epitaxial layer structures are probed using scanning capacitance microscopy.
Acquisition of scanning capacitance images over a wide range of bias voltages combined with theoretical analysis and numerical
simulation allows the presence, detailed nature, and possible structural origins of nanometer- to micronscale inhomogeneities
in electronic structure to be elucidated. Substantial lateral variations in local threshold voltages for transistor channel
formation are observed, at length scales ranging from submicron to >2 μm, and found to arise primarily from local variations
in AlxGa1−xN layer thickness. Features in electronic structure are also observed that are consistent with the existence of networks of
negatively charged threading edge dislocations, as might be formed at island coalescence boundaries during epitaxial growth.
The negative charge associated with these structures appears to lead to local depletion of carriers from the channel in the
AlxGa1−xN/GaN transistor epitaxial layer structure. 相似文献
13.
基于SiC衬底成功研制X波段0.25 μm栅长带有r栅场板结构的AlGaN/GaN HEMT,设计场板(field plate)长度为0.4 μm,0.6μm,0.7μm,0.9μm.研究了r栅场板长度及不同漏偏压下对器件直流,小信号特性及大信号的影响.器件直流I-V及转移特性并不依赖场板长度变化,增加场板长度器件击穿电压提高可达108 V,器件截止频率及振荡频率下降,输出功率大幅度提高,结合器件小信号提参结果分析.8 GHz下,总栅宽1 mm,场板长度为0.9 μm的器件,连续波输出功率密度7.11 W/mm,功率附加效率(PAE)35.31%,相应线性增益10.25 dB. 相似文献
14.
J. W. P. Hsu M. J. Manfra D. V. Lang K. W. Baldwin L. N. Pfeiffer R. J. Molnar 《Journal of Electronic Materials》2001,30(3):110-114
Scanning force microscopy was used to examine the surfaces of AlGaN/GaN heterostructures grown by molecular beam epitaxy (MBE)
on GaN templates prepared by hydride vapor phase epitaxy (HVPE). Away from dislocations, the MBE growth replicates the surface
morphology of the HVPE film, with monolayer steps clarly visible in topographic images. However, the surface morphology near
dislocations depends strongly on the MBE growth conditions. Under Ga rich growth the dislocations appear as hillocks, while
under stoichiometric growth they appear as pits. A dependence on Al concentration is also observed. Surface contact potential
variation near dislocations is consistent with excess negative charges surrounding by a depletion region, but this was observed
only for the film grown under stoichiometric conditions. 相似文献
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16.
Nucleation layer formation is a key factor for high quality gallium nitride(GaN)growth on a sapphire substrate.We found that the growth rate substantially affected the nucleation layer morphology,thereby having a great impact on the crystal quality,surface morphology and electrical properties of AlGaN/GaN heterostructures on sapphire substrates.A nucleation layer with a low growth rate of 2.5 nm/min is larger and has better coalescence than one grown at a high growth rate of 5 nm/min.AlGaN/GaN heterostructures on a nucleation layer with low growth rate have better crystal quality,surface morphology and electrical properties. 相似文献
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19.
S. K. Davidsson M. Gurusinghe T. G. Andersson H. Zirath 《Journal of Electronic Materials》2004,33(5):440-444
We have studied the influence of Al content, AlGaN layer thickness, and unintentional background doping by oxygen on the two-dimensional electron gas (2DEG) density in AlGaN/GaN heterostructures. Hall measurements were made on samples grown with molecular beam epitaxy. The 2DEG densities in the range 2–3×1013 cm?2 were measured. A one-dimensional Schrödinger-Poisson model was used to describe the heterostructure. The calculations gave two-dimensional electron densities in accordance with measured values. The electron density is very sensitive to the Al concentration in the AlGaN layer, whereas the sensitivity to layer thickness is small. Our simulations also showed that the two-dimensional concentration increased 50% when the free-carrier concentration changed from 1015 cm?3 to 1018 cm?3. The relation between donor concentration and free-carrier concentration was found to agree when using oxygen ionization energy as a parameter. 相似文献
20.
X.H. Wang X.L. Wang C. Feng C.B. Yang B.Z. Wang J.X. Ran H.L. Xiao C.M. Wang J.X. Wang 《Microelectronics Journal》2008,39(1):20-23
Pt/AlGaN/AlN/GaN high electron mobility transistors (HEMT) were fabricated and characterized for hydrogen sensing. Pt and Ti/Al/Ni/Au metals were evaporated to form the Schottky contact and the ohmic contact, respectively. The sensors can be operated in either the field effect transistor (FET) mode or the Schottky diode mode. Current changes and time dependence of the sensors under the FET and diode modes were compared. When the sensor was operated in the FET mode, the sensor can have larger current change of 8 mA, but its sensitivity is only about 0.2. In the diode mode, the current change was very small under the reverse bias but it increased greatly and gradually saturated at 0.8 mA under the forward bias. The sensor had much higher sensitivity when operated in the diode mode than in the FET mode. The oxygen in the air could accelerate the desorption of the hydrogen and the recovery of the sensor. 相似文献